A fibrous basic magnesium sulfate powder (which is also referred to as fibrous magnesium oxysulfate powder) is widely utilized as a filler for resin materials. A resin composition containing a fibrous basic magnesium sulfate powder dispersed therein generally shows improved physical properties such as improved flexural modulus and improved impact strength.
Japanese Patent Provisional Publication 56-149318 describes a process for preparing a fibrous basic magnesium sulfate powder which comprises the steps of dispersing magnesium hydroxide or magnesium oxide in an aqueous magnesium sulfate solution at a concentration of 25 wt. % or less, and subjecting the resulting dispersion to hydrothermal reaction at a temperature in the range of 100 to 300° C. In this patent publication, there is described a working example in which the resulting product (fibrous basic magnesium particles) is collected on filter and washed with water to obtain a fibrous basic magnesium sulfate powder.